ABSTRACT Approximately 1 in 5 U.S. college women is sexually assaulted (SA), and nearly half of these assaults involve alcohol. These assaults often occur in social settings, where others are present. Because of this, research has begun to focus on ways in which those who are a part of this social environment (?bystanders?) may be incorporated into assault prevention efforts. Seminal work by Latan and Darley (1970) underscores two conditions that must be in place in order for others in the social environment to take preventive action: a relationship with the potential victim, and a sense of personal responsibility to her. Without these, helping behavior is unlikely to occur. Typically offered in group format, to general audiences of students who may not socialize or even know one another, existing bystander-based interventions are unlikely to tap into the sense of relationship or responsibility that would catalyze action. This is a missed opportunity. In contrast, relationship and responsibility are the hallmark of friendships. Moreover, friends are central to the drinking context of college women and to the context of SA. For all of these reasons, friends are optimally positioned to act to prevent SA, and a focus on friends is a promising direction for intervention. Yet, data show that though women want to help protect their friends against SA, they report a number of barriers regarding whether, when, and how to do this. They also report lacking the necessary skills to intervene effectively. Thus, they do not feel ready to engage in SA prevention. A friend-based, motivational intervention can address these barriers, cultivating the relationship and responsibility that already exist between friends, and collaboratively addressing challenges that stand in the way of helping behavior. Accordingly, the objective of the proposed study is to develop an innovative, friend-based motivational intervention (FMI) that encourages and prepares friends to reduce SA risk. Delivered to pairs of friends (dyads), the FMI will be designed to foster collaborative efforts to increase readiness for, and decrease barriers to helping behavior, and to teach and plan together for assault prevention skills. As the role of alcohol has been under-addressed in SA prevention efforts, the FMI also will explicitly attend to how intoxication may serve as a barrier to friend intervention, and strategies for overcoming this barrier. The FMI will be developed in three stages (1. Development, 2. Implementation & Refinement, 3. Preliminary Testing). In the final stage of the project, the intervention will be tested in a randomized, controlled mini-trial (FMI vs. waitlist control). Friend dyads will be followed in bi-weekly online assessments for 3 months to examine changes in helping attitudes and behaviors. Feasibility, scalability, iatrogenic effects, and whether drinking influences intervention outcomes also will be examined. Findings will offer rich information about how best to incorporate friends into sexual assault prevention, and will lay the groundwork for the next steps for the FMI.